Emarginula sublaevis Schepman, 1908

Herbert, David G., 2024, The Vetigastropoda (Mollusca) of Walters Shoal, with descriptions of two new genera and thirty new species, European Journal of Taxonomy 923, pp. 1-119 : 15-16

Emarginula sublaevis Schepman, 1908

Fig. 6

Emarginula sublaevis Schepman, 1908: 91 , pl. 7 fig. 9.

Type loc.: Siboga stn 280, 8°17.4′ S, 127°30.7′ E (off eastern tip of Timor Island), depth 1224 m.

Emarginula sublaevis – Thiele 1913 in 1912–1919: 64, pl. 7. figs 16–17. — Hasegawa 2018: 143, figs 14g –j.

Material examined

WALTERS SHOAL – slopes • 2 empty shells, juvenile; stn DW4899; 33°09′ S, 44°02′ E; depth 707– 720 m; 6 May 2017; MNHN • 1 empty shell; stn DW4900; 33°10′ S, 44°01′ E; depth 660–670 m; 6 May 2017; MNHN • 1 living specimen; stn CP4901; 33°09′ S, 44°01′ E; depth 647–672 m; 6 May 2017; DNA tissue sample; MNHN-IM-2013-67271 • 1 living specimen; stn CP4902; 33°08′ S, 44°02′ E; depth 700–711 m; 7 May 2017; DNA tissue sample; MNHN-IM-2013-67272 .

Distribution

Japan and the central Indo-West Pacific to the south-western Indian Ocean. Collected on the slopes of Walters Shoal at depths of 670–707 m; trawled alive at depths of 672–700 m, on coarse substrata with abundant solitary corals, decapods and empty pteropod shells.

Remarks

This is the first record of Emarginula sublaevis from the Indian Ocean. Recently recorded from the Ogasawara Islands and Japan ( Hasegawa 2018), the species was previously known only from the holotype dredged off East Timor. The shell is distinctive on account of its relatively large size, coarsely lunulate selenizone with keeled lateral margins ( Fig. 6C ) and extremely fine sculpture ( Fig. 6D ). The original figure of the holotype provided by Schepman (1908) rather exaggerates the strength of the radial sculpture, but the photograph of the same specimen provided by Hasegawa (2018) gives a more realistic depiction. The intritacalx pits are small and simple, dividing progressively with growth as intermediary radial ribs (secondary to quaternary) arise by intercalation between the primary ribs, though there is little difference in rib strength at the shell margin.

The specimens from the Walters Shoal have a slightly narrower basal profile than the holotype (L/W 1.48–1.54 vs 1.37 in holotype) and the apex lies somewhat closer to the posterior margin, but such differences are trivial when considered in terms of the extent of intraspecific variation shown in some other species of Emarginula . Though geographically distant from the central Indo-West Pacific records, I can find no grounds to consider the Walters Shoal material a distinct species.

Emarginula poppeorum Romani & Crocetta, 2017 [= E. gigantea Poppe, 2008 , non Coquand, 1859, nec Seguenza, 1863] is evidently a related species of even larger size, attaining a length of up to 55 mm ( Poppe & Tagaro 2020). Hasegawa (2018) considered E. hosoyai Habe, 1953 to be a synonym of E. sublaevis , but more recently, Poppe & Tagaro (2020) treated it as distinct.

Figures

Fig. 6. Emarginula sublaevis Schepman, 1908. A–B. Dorsal and side views, Walters Shoal, stn CP4901, base 15.6 × 10.1 mm, height 8.3 mm (MNHN-IM-2013-67271). C–D. Detail of selenizone morphology and shell sculpture, Walters Shoal, stn DW4900 (MNHN). Scale bars= 1.0 mm.